The I/O PCB status code is set by IMS™ in response to the IMS calls that the Assist module makes on behalf of the server. For example, GU and GN calls usually result in bb, QC, or QD status codes. However, when the Assist module detects a TCP/IP error, it sets the status code field of the I/O PCB to ZZ with further information about the error in the reserved field of the I/O PCB. This field should be initially tested as a signed, fixed binary halfword:

• If the halfword is positive, then a socket error has occurred, and the field should continue to be treated as a signed fixed binary halfword. The field contains the 2 low-order bytes from the ERRNO resulting from the socket call. (See Return codes).
• If the halfword is negative, then an IMS or other type of error has occurred, and the field should be treated as a fixed-length, 2-byte character string containing one of the following information:

  Code

  Meaning

  EA

  A call that used the AIB interface to determine the I/O PCB address failed.

  EB

  The output buffer is full. An attempt was made to insert (ISRT) more than 32KB (including the segment length and reserved bytes) to be sent to the client.

  EC

  A QD status code was received in response to a GU or ROLB call when attempting to retrieve the first segment of data after the transaction-initiation message (TIM) segment. This implies that the client sent only the TIM segment followed by an end-of-message segment with no actual data segments.